During the fabrication of magnetic heads for use in magnetic data storage applications, a plurality of transducers and auxiliary circuits are typically fabricated on a common substrate. To establish adequate performance for high efficiency recording heads, it is desirable that features of the magnetic head, such as the height of a magnetoresistive element (MRE) sensor or a throat height of a write pole are controlled within a very tight tolerance.
Thin film deposition techniques are often used to fabricate magnetic read/write transducers. In a typical process, an array of transducers and electronic lapping guides (ELGs) are formed on a common substrate by a deposition of metallic and nonmetallic layers. The patterning of the array of transducers and ELGs can be accomplished using photolithography in combination with etching and lift-off processes. The finished array or wafer can be optically and electrically inspected and then sliced to produce bars, with one row of transducers in a side-by-side pattern on each bar. The bars are then lapped at the air bearing surface (ABS), which will eventually face the recording medium, to establish a specified sensor height.
During machining of a particular row of transducers and ELGs, the machined surface moves from a beginning position to a final position while reducing the height of the transducers. The primary function of the ELGs is to control the machining process such that the desired transducer height is achieved. After a particular row of transducers is machined to the desired transducer height as controlled by the ELGs, the rows or bars are cut or diced into individual recording heads or sliders.
Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. For heat assisted magnetic recording (HAMR) a tightly confined, high power laser light spot is used to preheat a portion of the recording medium to substantially reduce the coercivity of the heated portion. Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion. In this manner the coercivity of the medium at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells.
Although the electronic lapping guides are useful to lap recording heads to a target transducer height, there is no easy way to verify whether all the separate layers of a HAMR head are actually aligned both in a direction perpendicular to the ABS and in a cross-track direction. It would be desirable to determine the location of the elements in a HAMR recording head at the air bearing surface of the recording head.